The present invention disclosed herein relates to a vibration transducer and an implantable hearing aid device.
Recently, hearing loss population in the whole world is continuously increasing due to industrialization and wide prevalence of sound systems having excellent performance. The hearing loss population may be largely classified into three major groups. The first one is a mild and moderate hearing loss group in which the hearing loss is solved with the aid of existing hearing aid devices. The second one is a moderately severe and severe hearing loss group in which the hearing loss is not easily solved with the aid of the existing hearing aid device. The third one is a profound hearing loss and congenital hearing impairment group in which the hearing loss or hearing impairment is solved only by using a cochlear implant. Here, a hearing loss solution for the moderately severe and severe hearing loss group accompanied by sensorineural hearing loss is relatively poor in comparison to other groups, and thus a lot of people having hearing loss are suffering.
Thus, various implantable hearing aid device models targeting the moderately severe and severe hearing loss group accompanying the sensorineural hearing loss are being studied throughout the world. Here, a middle ear implant is a hearing aid device in which auditory ossicles are forcibly vibrated to allow a wearer to hear a sound. The middle ear implant fields are most actively studied at the present, and a portion of the devices in the middle ear implant fields has been succeeded in commercialization. A model that is successfully settled in the present hearing aid device market is Vibrant Soundbridge developed by MED-EL company (Austria). The Vibrant Soundbridge uses a floating mass transducer (FMT) installed in the auditory ossicles as a transducer. Although various implantable hearing aid devices are being studied, there are still more requirements to be developed in performance so as to have a bigger share of the market in the world. Among those requirements, since a vibration transducer is a key factor that determines a characteristic of the implantable hearing aid device as an output unit of the middle ear implant, it may not be emphasized that the necessity of the vibration transducer having large vibration displacement and operating by low power.
Recently, it is being pointed out that when the FMT is installed into an incus, the incus is vulnerable to longterm safety. Clinically, these limitations are left unresolved. As an alternative, studies for a transducer directly applying vibration stimulus to a round window are widely underway in the academic world. When the transducer is driven in the round window, the transducer may not strain the auditory ossicles and be used in cases in which the auditory ossicles are destroyed due to chronic otitis media, or it is difficult to apply vibration to an oval window.
There are two types of round window driving vibration transducers. The existing FMT may be installed into the round window, and a MET transducer of Carina device that is being developed by Otologics company may be used to vibrate the round window. Additionally, there are Korean Patent Registration No. 10-0859979, which is entitled “Implantable Middle Ear Hearing Device with Tube Type Vibration Transducer” and has been suggested by Cho, Jin-ho and so on, Korean Patent Registration No. 10-0931209, which is entitled “Round Window Vibration Transducer with Easy Attachment Method and Implantable Hearing Aid Using the Transducer”, and Korean Patent Registration No. 10-1223693, which is entitled “Round Window Driving Vibrator of Three-Coils Type with Excellent Driving Force”.
However, when the vibration transducer is installed into the round window in the FMT method, vibration efficiency is poor at low frequency, because the FMT's amount of vibration is proportional to the mass acceleration of its magnet in the housing. Also, since the vibration transducer is affected by the external magnetic fields, the round window may be damaged in strong magnetic field environments such as MRI, or the transducer may get out of the round window. Also, since the MET transducer of Otologics company having a flat frequency characteristic in an audible range has a large scale, it may be difficult to secure a range of vision with respect to the round window during surgery. Thus, it is necessary to use a separate tip for contacting the round window. Also, the MET transducer may be affected by the external strong magnetic fields.
The round window drive-type tube vibration transducer disclosed in Korean Patent Registration No. 10-0859979 is driven by a manner using air or a fluid pressure generated in a tube. However, when an end of the tube has an opening, the opening is likely to be blocked by a body fluid exuding from an inner ear. Thus, the transducer may be deteriorated in performance when the transducer is continuously used. To solve the limitation, the end of the tube is treated as a diaphragm, and the round window vibrates by using the vibration of the diaphragm in Korean Patent Registration No. 10-0859979. However, since the diaphragm vibrates in a dome shape, a portion of area of the diaphragm contacts the round window. Thus, there is a limitation in that vibration energy is effectively transmitted into a cochlear. Therefore, to install a tube-type vibrator finished by using the diaphragm, there is a method in which a surgical drill is used to expand a niche portion of the round window, and a contact area between the vibrator and the round window is increased by using fascia tissue as a medium. When the diaphragm excessively increases in diameter to increase vibration transmission efficiency of the tube-type vibrator having the diaphragm, the transmission efficiency of the vibration energy may increase. However, the immoderate expansion of the niche of the round window may damage the cochlea, resulting from surgery. Also, since the vibration transducer using the diaphragm has to depend on only a thickness and diameter of the diaphragm to adjust the frequency characteristic, it may be difficult to precisely control the frequency characteristic.